Hi TFN, the most vulnerable structures are the glenoid, the labrum, the superior biceps anchor to the labrum and of course the Wikipedia reference-linkrotator cuff tendons and muscles. It is hard to say exactly but a lack ROM or pain with IR or HBB could be related to a pathologic or inflamed biceps tendon and/or superior labrum (SLAP), pathology or weakness of subscapularis, or just protective spasm and inhibition within the rotator cuff as a result of the trauma to the shoulder. Your ROM despite the pain you experience is very good compared to myself say for example. Based on your brief history and that of your brother you may be one who is susceptible to ongoing shoulder instability especially if AFL is your game. In the absence of significant pathology the activation, control and then strengthening of the rotator cuff is the key to shoulder stability. Your cuff right now will be inactive, inhibited and only partially functional during active movements and will struggle to control those movements at end of range positions. The best advice I can give is start now but also don't forget the scapula as it's position during cuff loading is very important to achieve stability also. At the end of the day you may need someone who is solely focused on the shoulder for the best results.
All the Best!
Luke